Moving blade for a turbomachine, the blade having a common cooling air feed cavity

ABSTRACT

A moving blade for a turbomachine, the blade comprising an aerodynamic surface extending radially between a blade root and a blade tip, and at least one internal cooling circuit made up of at least one radial cavity, at least one air admission opening formed in the blade root and opening out into the cavity(ies), and a plurality of outlet orifices opening out from the cavity(ies) and leading to the outside of the blade, the blade root having lower swellings and upper swellings defining bearing surfaces for fastening the blade to a rotor disk. The air admission openings of the cooling circuit(s) open out into a common cavity that is formed in the blade root and that extends radially from the base of the blade root at least as far as the upper swelling of said root.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of cooling moving blades in a turbomachine, and in particular the moving blades of the high-pressure turbine.

It is known to provide the moving blades of a gas turbine in a turbomachine, such as the high-pressure or the low-pressure turbine, with internal cooling circuits enabling them to withstand without damage the very high temperatures to which they are subjected while the turbomachine is in operation. Thus, for a high-pressure turbine, the temperature of the gas coming from the combustion chamber can reach values much higher than those that the moving blades of the turbine can withstand without damage, which has the consequence of limiting the lifetime of the blades.

By means of such cooling circuits, air that is introduced into the blade via its root travels through the blade, following a path formed by a plurality of cavities formed in the blade, prior to being ejected through outlet orifices that open out in the surface of the blade.

Fabricating a gas turbine moving blade having a cooling circuit of that type by a casting process presents drawbacks. A blade of that type is generally obtained by casting a metal into a mold that contains a ceramic core having the function of reserving a location for each of the cavities constituting the cooling circuits of the blade. Unfortunately, the large number of cavities needed for cooling the blade makes it difficult to provide a ceramic core that is robust. There is therefore a significant risk that such a core will break.

Furthermore, given the particular shape of a gas turbine moving blade, a given cavity in a cooling circuit does not lie in a single plane; the portion of the cavity situated at the root of the blade is offset from the remainder of the cavity. In other words, the cavities are curved. A result of this curvature of the cavities is that the flow of air in the cavities is disturbed, and that impedes cooling the blade.

OBJECT AND SUMMARY OF THE INVENTION

A main object of the present invention is thus to mitigate such drawbacks by providing a moving blade provided with internal cooling circuits that are simpler to fabricate by casting and in which the flow of air is facilitated.

This object is achieved by a moving blade for a turbomachine, the blade comprising an aerodynamic surface extending radially between a blade root and a blade tip, and at least one internal cooling circuit made up of at least one radial cavity, at least one air admission opening formed in the blade root and opening out into the cavity(ies), and a plurality of outlet orifices opening out from the cavity(ies) and leading to the outside of the blade, the blade root having lower swellings and upper swellings defining bearing surfaces for fastening the blade to a rotor disk, wherein the air admission openings of the cooling circuit(s) open out into a common cavity that is formed in the blade root and that extends radially from the base of the blade root at least as far as the upper swelling of said root.

The process of fabricating such a blade by casting is simplified. The ceramic core is consolidated by the presence of the location reserved for the common cavity for feeding air to the cavities of the cooling circuit(s). Furthermore, the presence of such a common cavity in the blade root avoids curving the cavities of the cooling circuit(s), thereby improving the flow of air therein. In addition, the presence of the common cavity makes it possible to make blades having a large cross-section—and thus an enlarged root—without thereby significantly increasing their weight (the purpose of using blades having a large cross-section is to reduce the total number of the moving blades in a given stage of a gas turbine).

According to an advantageous characteristic of the invention, the common cavity has keying means for ensuring that a plate for calibrating the flow rates of air fed to the cavities of the cooling circuit(s) cannot be installed the wrong way round.

The common cavity may be open in part through an upstream wall so as to facilitate feeding air to said common cavity.

The end wall of the common cavity may be inclined from upstream to downstream relative to the base of the blade root in such a manner as to facilitate feeding air to said common cavity.

Said common cavity may include a radial wall forming a stiffener disposed so as to subdivide the cavity into at least two sub-cavities.

The invention also provides a turbomachine, and a high-pressure turbine for a turbomachine, each including a plurality of moving blades as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings which show an embodiment having no limiting character. In the figures:

FIG. 1 is a longitudinal section view of a moving blade of the invention;

FIGS. 2A and 2B are fragmentary perspective views of the root of the FIG. 1 blade; and

FIGS. 3A and 3B are fragmentary section views of moving blades constituting other embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1, 2A, and 2B show a moving blade 10 for a turbomachine, such as a moving blade of a high-pressure turbine. Naturally, the invention can also be applied to other moving blades of the turbomachine, for example to the low-pressure turbine blades thereof.

The blade 10 has an aerodynamic surface that extends radially between the blade root 12 and a blade tip 14. This aerodynamic surface comprises a leading edge 16 placed facing the flow of hot gas coming from the combustion chamber of the turbomachine, a trailing edge 18 opposite to the leading edge 16, a pressure side face, and a suction side face, the side faces (not shown in the figures) interconnecting the leading edge 16 and the trailing edge 18.

The blade 10 also has two lower swellings (or teeth) 12 a disposed laterally on either side of the blade root 12 and two upper swellings 12 b also disposed laterally on either side of the root, these swellings 12 a, 12 b defining bearing surfaces for fastening the root in a slot in a rotor disk (not shown). The section of the blade root defined between the lower and upper swellings 12 a and 12 b is referred to as a lower neck 12 c, and the section defined between the upper swellings 12 b and the bottom face of the platform 12 e of the root is referred to as an upper neck 12 d.

In known manner, the blade 10 has at least one internal cooling circuit. This circuit comprises one or more cavities 20 extending radially over the full height of the blade, one or more air admission openings 22 formed in the blade root 12 and leading to the cavity(ies) 20, and a plurality of outlet orifices 24 opening out from the cavity(ies) and leading to the outside of the blade.

In the embodiment of FIG. 1, there are four internal cooling circuits for the blade 10: one circuit situated in the vicinity of the leading edge 16 of the blade and formed by two radial cavities 20 a that are fed from an air admission opening 22 a; two circuits situated in the central portion of the blade, one of them being formed by three radial cavities 20 b that are fed by an air admission opening 22 b, and the other being formed of two radial cavities 20 c that are fed by an air admission opening 22 c; and a circuit situated in the vicinity of the trailing edge 18 of the blade and formed by a radial cavity 20 d which is fed by an air admission opening 22 d.

All of the cooling circuits are also provided with outlet orifices, respectively referenced 24 a to 24 d, that open out from the radial cavities 20 a to 20 d and lead to the outside of the blade. Naturally, the number of cooling circuits and the quantities of radial cavities, air admission openings, and outlet orifices making up each of the circuits could be different.

The blade 10 is typically obtained by casting a metal in a mold containing a ceramic core that has the function of occupying the positions of the radial cavities 20 or of the internal cooling circuits of the blade

According to the invention, the air admission openings 22 of the internal cooling circuit(s) of the blade 10 all open out into a common cavity 26 formed in the blade root 12.

The presence of such a common cavity 26 in the blade root presents numerous advantages. Firstly, the process of fabricating the blade by casting is simplified. The dimensions of this common cavity ensure that the ceramic core needed for this type of fabrication process is consolidated in the location reserved for the common cavity. In addition, the presence of a common cavity makes it possible to improve the flow of air in the cavities of the blade cooling circuit. Finally, the presence of the common cavity makes it possible to make a blade with an enlarged root without significantly increasing its weight.

The common cavity 26 may present a shape that is substantially in the form of a rectangular parallelepiped, as shown in FIGS. 1, 2A, and 2B. By way of example, such a common cavity may present a section area of about 2000 square millimeters (mm²), the cavities of the cooling circuit(s) generally having sections of about 4 mm² to 30 mm².

As shown in FIG. 1, the common cavity 26 extends radially from the base 12 f of the blade root 12 at least as far as the upper swellings 12 b thereof. This disposition makes it possible to obtain a cavity that is “tall”, thereby limiting head losses in feeding the cooling cavities 20 a to 20 d. In addition, the feed of cooling air to the cavities is more uniform.

According to an advantageous characteristic of the invention, the common cavity 26 has keying means 28 to ensure that a plate 30 for calibrating the flow rates of air feeding the cavities 20 or the internal cooling circuit(s) of the blade can be fitted in a correct orientation only.

The use of a plate 30 for calibrating the flow rates of air feeding the cavities or the internal cooling circuit(s) of a blade is well known in itself. Typically, it is constituted by a metal plate 30 that is secured (e.g. by brazing or welding) to the base of the blade root. The plate 30 is pierced by calibration holes 32 that are placed in register with the air admission openings once the plate is in position. Depending on the sections of the holes 32 in the plate, it is thus possible to calibrate accurately the flow rates of air fed to the cavities of the internal cooling circuit(s) of the blade.

In the context of the invention, such a calibration plate 30 is fastened at the end 26 a of the common cavity 26 as shown in FIGS. 3A and 3B. The advantage of mounting the calibration plate at the end of the common cavity is that it enables air flow to become uniform in the common cavity before feeding the radial cavities or the cooling circuit(s).

In order to provide keying for said calibration plate 30 (in order to ensure that the plate is not mounted the wrong way round), the plate 30 presents a cutout 34 (e.g. formed at one of its corners, as shown in FIG. 2B), and the common cavity 26 presents, in right section, a shape that is substantially identical to the shape of the plate (in FIG. 2B, one of the corners of the cavity has additional matter 28 of a shape that is complementary to the cutout 34 in the plate).

It can easily be understood from FIG. 2B that it is not possible to mount the calibration plate 30 the wrong way round. Thus, any risk of error in calibrating the flow rates of air feeding the cavities or the internal cooling circuit(s) of the blade is avoided.

FIGS. 3A and 3B show two other embodiments of the common cavity of the moving blade of the invention. In these figures, the moving blade 10′, 10″ is mounted between a downstream plate 36 and an upstream plate 38, and the cooling circuits of the blade are fed with air via the upstream plate 38, as represented by the arrow.

In the variant embodiment of FIG. 3A, the common cavity 26 formed in the root 12 of the blade 10′ for feeding air to the cavities of the internal cooling circuits is open in part level with the upstream wall 26 b so as to facilitate feeding air thereto.

In the variant embodiment of FIG. 3B, the end wall 26 a of the common cavity 26 formed in the root 12 of the blade 10″ for feeding air into the cavities of the internal cooling circuits slopes from upstream to downstream relative to the base 12 f of the blade root so as to facilitate feeding air to the cavity.

Naturally, these two variant embodiments for the common cavity can be combined: it may be open in part level with its upstream wall and it may have an end wall that slopes from upstream to downstream relative to the base of the blade root.

In yet another variant embodiment of the common cavity (not shown in the figures), the common cavity may have a radial wall which is disposed to subdivide the common cavity into two sub-cavities. Such a radial wall makes it possible to provide a stiffener for the common cavity so as to improve its mechanical behavior. 

1. A moving blade for a turbomachine, the blade comprising an aerodynamic surface extending radially between a blade root and a blade tip, and at least one internal cooling circuit made up of at least one radial cavity, at least one air admission opening formed in the blade root and opening out into the cavity(ies), and a plurality of outlet orifices opening out from the cavity(ies) and leading to the outside of the blade, the blade root having lower swellings and upper swellings defining bearing surfaces for fastening the blade to a rotor disk, wherein the air admission openings of the cooling circuit(s) open out into a common cavity that is formed in the blade root and that extends radially from the base of the blade root at least as far as the upper swelling of said root.
 2. A blade according to claim 1, wherein the common cavity has keying means for ensuring that a plate for calibrating the flow rates of air fed to the cavities of the cooling circuit(s) cannot be installed the wrong way round.
 3. A blade according to claim 1, wherein the common cavity is open in part through an upstream wall so as to facilitate feeding air to said common cavity.
 4. A blade according to claim 1, wherein the end wall of the common cavity is inclined from upstream to downstream relative to the base of the blade root in such a manner as to facilitate feeding air to said common cavity.
 5. A blade according to claim 1, wherein said common cavity includes a radial wall forming a stiffener disposed so as to subdivide the cavity into at least two sub-cavities.
 6. A turbomachine high-pressure turbine, including a plurality of moving blades according to claim
 1. 7. A turbomachine, including a plurality of moving blades according to claim
 1. 